Antenna element for anti-theft devices

Abstract

 An antenna element (33) for anti-theft devices (10, 11) of the type affecting a magnetic, acoustic or electromagnetic field, has two antennas (35) projecting from opposite sides of said element and forms together with said antennas a configuration similar to the letter S.

Description

[0001] The invention relates to an antenna element for anti-theft devices of the type affecting a magnetic, acoustic or electromagnetic field, which is maintained between bow-shaped antennas at the exit of a shop, to disturb the field and cause signal generation.

[0002] The antenna element of the invention has obtained the characteristics of claim 1.

[0003] In order to explain the invention in more detail an embodiment thereof will be described below reference being made to the accompanying drawing in which

FIG. 1 is a fragmentary perspective view of a spectacle frame provided with an anti-theft device, and

FIG. 2 is view of a cover from the back side thereof which is attached to the anti-theft device and is provided with the antenna element of the invention.

[0004] The anti-theft device in FIG. 1 comprises a sleeve 10 open at one end thereof, which has rectangular cross-sectional shape and preferably is made of plastics, for example polycarbonate. On one broad side thereof the sleeve is provided with a cover 11 of the same material as the sleeve, said cover being attached to the sleeve by ultrasound welding. The sleeve 10 has opposing longitudinal slots 12 in the two narrow sides thereof, which are big enough to allow the bow 14 of a spectacle frame 13 to be passed through the slots. Clamping means is provided in the sleeve 10, and the body formed by sleeve 10 and cover 11 is mounted to the bow, and is demounted from the bow by using a special tool, which can be engaged with said clamping means.

[0005] Inside the body there is located an element 33 (a so-called "diode") of the type affecting a magnetic, acoustic or electromagnetic field maintained between bow-shaped antennas at the exit of a shop, to disturb the field and cause signal generation. Said element is mounted inside the cover 11, and for this purpose the cover has on the backside thereof four small pins 34 between which the element 33 is located while antenneas 35 of flexible wire provided on the element are passed around other, large pins 36 on the backside of the cover. When the cover 11 is attached to the sleeve 10 the pins are positioned adjacent the outside surface of the sleeve such that the element is held in a well defined position. As will be seen from FIG. 2 the antenna element of the invention formed by element 33 and antennas 35 has a configuration similar to the letter S when mounted to cover 11.

Claims

1. Antenna element for anti-theft devices (10, 11) of the type affecting a magnetic, acoustic or electromagnetic field, characterized in that the element (33) and two antennas (35) projecting from opposite sides of said element form together a configuration similar to the letter S.

2. Antenna element as in claim 1 characterized in that it is mounted to the backside of a cover (11) forming part of an anti-theft device (10, 11).

3. Antenna element as in claim 2 characterized in that the configuration of the antenna element is defined by projections (34, 36) on the cover (11).

Drawing